1. Field of the Invention
The present invention relates to an ophthalmic ultrasonic diagnostic apparatus which diagnoses an eyeball by obtaining information on constituent parts inside the eyeball such as an axial length and a corneal thickness.
2. Description of Related Art
There is known an ophthalmic ultrasonic diagnostic apparatus which obtains information on constituent parts inside an examinee's eye by emitting an ultrasonic wave from an ultrasonic transducer incorporated in a probe and performing processing on echoes reflected respectively from tissues of constituent parts of the eyeball. This apparatus uses the A-mode method by which the reflected echoes from the tissues are displayed as a waveform, and the lengths of the constituent parts such as an axial length and a corneal thickness are calculated (for example, see Japanese Patent Application Unexamined Publication No. 2001-187022).
This kind of apparatus performs automatic measurement in which only a measurement value which falls within a width of permissible dispersion out of sampled results is determined as effective data when the calculated axial length and other lengths are displayed and the measurement is automatically terminated when a predetermined number (e.g. ten) of the effective data is obtained.
A program for the automatic measurement is, for example, set as follows. First, a width of permissible dispersion with reference to a sampled measurement value is determined by the program. Then, if ineffective data that a measurement value falls out of the width is obtained successively three times, the measurement value based on which the width has been initially determined is regarded inappropriate. Then, the measurement values which have been already obtained are abandoned. Then, with reference to a newly sampled measurement value, measurement values which are sampled thereafter are processed in the same manner as above. This is because the program is set based on an idea that the probe generally touches the cornea of the examinee's eye strongly in an early stage of the measurement in which the probe starts to touch the cornea, so that the measurement values of the axial length and the corneal thickness tend to be measured smaller though the measurement values gradually become stable.
However, if a measurer (examiner) is unskilled and cannot make the probe touch the cornea in a stable condition, the measurement values may be dispersed also after the early stage of the measurement, which takes time until the measurement is terminated. Lengthy measurement puts a burden on the examinee and the examiner. A solution to the problem is to reduce the number of conditions for automatic termination (e.g. to reduce the number from ten to three) if the conditions for measurement termination are not satisfied even after a predetermined period of time. However, from the view point of reliability of the measurement result, it is preferable that the number of the conditions is larger.